Embodiments of the present invention relate to a dispensing unit capable of circulating a fluid and a method for circulating a fluid.
Today, diesel powered vehicles account for large emissions of nitrogen oxides, generally referred to as NOx. The NOx emissions are harmful to the environment, implying that several techniques are used in order to try to reduce these emissions.
One technique used to reduce the amount of harmful NOx emissions is selective catalytic reduction (SCR). The basic idea of SCR is to convert NOx into harmless diatomic nitrogen (N2) and water (H2O). The reaction is enabled using a reductant which is added onto a catalyst. Several reductants may be used such as anhydrous ammonia, aqueous ammonia or urea.
Today a standard is established for using a SCR reductant in diesel powered vehicles. The reductant used is an aqueous urea solution having a urea concentration of 32.5%. The solution is referred to as AUS32. In order to obtain the correct concentration the urea is mixed with demineralized water.
When the diesel engine is running AUS32 is added into the exhaust flow, before or in the catalytic converter, by an amount corresponding to 3-5% of the diesel consumption. When AUS32 is added to the exhaust flow of a diesel engine, the engine can be operated more intensely without generating more NOx emissions.
In Europe AUS32 is generally sold under the trade mark of AdBiue® and in North America the trade name for AUS32 is Diesel Exhaust Fluid or DEF.
AUS32 is commonly available at service stations throughout the world. Various kinds of dispensers are used in order to refill AUS32 in the therefore intended tanks of diesel powered vehicles.
There are however several problems related to the refilling and storing of AUS32. For instance, the AUS32 fluid will easily crystallize when subjected to air i.e. when dried out. This implies that crystals will begin to build up at nozzles and other parts of the dispensers that are not tightly sealed from air. This means in practice that clogging leading to a reduced flow will become a problem.
Another even more severe problem encountered in dispensers for AUS32 is crystallization by freezing of the fluid. The AUS32 fluid will begin to crystallize at −7° C., forming a slush. At −11° C. the fluid will freeze forming a solid. Once the temperature drops below −7° C. it is critical to control the environment of the parts of the dispensers which are subjected to the AUS32 fluid. A common solution used to counteract the fluid from freezing is to place all parts of the dispenser subjected to the fluid in a controlled heated environment. This solution makes the refilling considerably more complicated for the user, since the refilling hose and nozzle must in practice be placed in a heated cabinet or similar. During a refilling process the user must thus open the cabinet before being able to refill the AUS32 tank of his/her vehicle. Once finished the user must close the cabinet in order to not risk that the fluid in the refilling hose will freeze. If the cabinet is not sufficiently closed after a refilling process the fluid in the refilling hose and nozzle might freeze, leaving the dispenser useless for the next user. The use of heated cabinets does also bring about considerable energy consumption, particularly when the cabinet is not sufficiently closed after a refilling process.
AUS32 is also often sold in cans. By providing AUS32 in cans, the fluid can be prevented from freezing during storage, by for example storing the cans in a controlled environment, such as inside a service station. The use of cans filled with AUS32 brings about different problems. The user will for example have to open the can manually and thereafter pour the AUS32fluid into the therefore intended tank of a vehicle. This means that there is a significant risk of spilling AUS32 during the refilling.